1. Field of the Invention
The present invention is related to a steering column assembly and more particularly to a steering column assembly which reduces undesirable passenger compartment noise.
2. Description of the Prior Art
A recent trend in automobile design is to decrease passenger compartment noise in order to make driving more enjoyable. Passenger compartment noise is noise detected in the passenger compartment of an automobile and is comprised of external noise and internal noise. External noise originates from sources located outside of the passenger compartment; for example, noise produced by the automobile's engine and tires, and noise produced by traffic. Internal noise is generated by devices located in the passenger compartment. In the past, the external noise component of passenger compartment noise was significantly greater than the internal noise component. As such, clicks and squeaks of switch mechanisms located in the passenger compartment of an older automobile are typically "drowned out" by external noise. More recently, however, several technologies have been combined to reduce external noise by, for example, reducing engine noise and incorporating sound-proofing materials into the automobile body to block traffic noise. As the external noise component of passenger compartment noise is decreased, the clicks and squeaks associated with internal noise devices become more noticeable and irritating.
Therefore, in order to further reduce passenger compartment noise, there is a need for mechanisms located in the passenger compartment which exhibit silent operation.
FIG. 1 shows an exploded perspective view of a typical prior art steering column assembly 1. The steering column assembly 1 includes a lock fixture 10 connected to a steering column (not shown), a steering shaft 20 rotatably mounted within the steering column and having an end portion extending through the lock fixture 10, a switch assembly 30, an upper housing 40, a lower housing 45 and a clock spring connector 50 mounted on the lock fixture 10, and a steering wheel 60 mounted on the steering shaft 20. The lock fixture 10 includes a front plate 11, a pair of vertical posts 12 extending from an upper edge of the front plate 11, and a pair of horizontal flanges 13 located on opposite sides of the front plate 11. The switch assembly 30 is mounted on the vertical posts 12, and the horizontal flanges 13 receive a screw connecting the upper housing 40 and the lower housing 45. The clock spring connector 50 is snap-coupled to a front surface of the front plate 11 over the steering shaft 20. Finally, the steering wheel 60 is fixedly connected to the steering shaft 20 and engages the clock spring connector 50 as described below.
FIG. 2 shows an enlarged perspective view illustrating the clock spring connector 50 and a portion of the steering wheel 60 of the steering column assembly 1. The clock spring connector 50 includes a fixed member 51 and a movable member 52 rotatably connected to the fixed member 51. An engaging portion 61 is connected to and extends from the steering wheel 60. When the steering wheel 60 is connected to the steering shaft 20, the engaging portion 61 is received within the recess 53, and manual rotation of the steering wheel 60 produces a concomitant rotation of the movable member 52 relative to the fixed member 51.
FIG. 3 shows a simplified front section view illustrating the connection between the engaging portion 61 and the recess 53. A clearance C of approximately 1.5 mm is provided between the engaging portion 61 and the recess 53 to facilitate assembly. When the steering wheel 60 is rotated from the position indicated by solid lines to the positions 61(1) and 61(2) indicated by dashed lines, the engaging portion 61 rotates an angle .THETA. of approximately 5.degree. without contacting the walls of the recess 53. As such, a range of free motion of the steering wheel 60 is present in the steering column assembly 1. Of course, when the steering wheel 60 is turned beyond the angle .THETA., the engaging portion 61 presses against the walls of the recess 53, thereby rotating the movable member 52 relative to the fixed member 51.
FIGS. 4(a) and 4(b) show top and side views, respectively, of the clock spring connector 50 connected to the lock fixture 10. Referring to FIG. 4(a), the clock spring connector 50 includes an upper locking finger 54 and a lower locking finger 55. As best illustrated in FIG. 1, the lock fixture 10 includes an opening 14 and a slot 15 formed on the front plate 11. In addition, the lock fixture 10 includes an upper vertical flange 16 and a lower vertical flange 17 located behind the front plate 11. The opening 14 and the receiving slot 15 are formed with a width W which provides a clearance of approximately 3 mm between the locking fingers 54, 55 and the opening 14 and slot 15 to facilitate assembly. When the clock spring connector 50 is connected to the lock fixture 10, the upper locking finger 54 extends through the opening 14 and is held by the upper vertical flange 16. Similarly, the lower locking finger 55 extends along the receiving slot 15 and is held by the lower vertical flange 17.
A problem with the above-described prior art steering column assembly 1 is that the clearance C between the engaging portion 61 and the recess 53 results in a clicking noise when the steering wheel 60 is rotated. Referring to FIG. 3, when the engaging portion 61 is rotated from the position 61(1) to the position 61(2), the resulting collision between the engaging portion 61 and the recess 53 generates an audible click which can be heard in the passenger compartment of an automobile.
Another problem associated with the prior art steering column assembly 1 is that the clearance between the engaging portion 61 and the recess 53 reduces the sensitivity of a turn signal canceling mechanism. The turn signal canceling mechanism (not shown) is mounted on the switch assembly 30 and is actuated by rotation of the movable member 52. Because of the range of free motion due to the clearance C, discussed above, actuation of the turn signal canceling mechanism is delayed after each turn until the steering wheel 60 is rotated through the angle .THETA., as shown in FIG. 3.
Another problem associated with the prior art steering column assembly 1 is that the fixed member 51 shifts relative to the lock fixture 10 due to the clearance provided between the locking fingers 54, 55 and the opening 14 and slot 15, thereby creating noise. That is, as the steering wheel is turned, friction between the movable member 52 and the fixed member 51 causes the fixed member 51 to move relative to the lock fixture 10 until the upper finger 54 and the lower finger 55 abut the edges of the opening 14 and the slot 15. This relative movement causes audible noises which can be heard in the passenger compartment.
Still another problem associated with the prior art steering column assembly 1 is that the upper locking finger 54 can become cracked or damaged before mounting onto the lock fixture 10. That is, the clock spring connector 50 includes a rigid socket structure 56 (FIG. 4) which is located near the lower locking finger 55. The socket housing 56 protects the lower locking finger 55 during handling prior to assembly. However, the upper locking finger 54 is not protected and can be cracked prior to assembly, and then broken-off during use, thereby producing a loud noise each time the turn signal canceling mechanism is activated.